The compression algorithms for the System.IO.Compression.DeflateStream and System.IO.Compression.GZipStream classes have improved so that data that is already compressed is no longer inflated. This results in much better compression ratios.

Uh huh. Let's test that, shall we? :)

We'll use a revised version of the C# test program I used the last time, one which feeds an entire buffer to the compressor. This is necessary since GZipStream is unfortunately sensitive to write block sizes: